Internal-combustion engine



A. c. NESFIELD INTERNAL-COMBUSTION ENGINE Filed Feb. 18, 1944 sSheets-Sheet 1 Feb 13, '1945. A. c. NESFIELD 2,369,245

INTERNAL-COMBUSTION ENGINE- Filed Feb. 18, 1944 s'sheezs-sheet 2 I nue rFeb. 13,1945. c NESHELD 2,369,245

INTERNAL- COMBUSTION ENGINE Filed Feb. 18, 1944 s Sheets-Sheet 3 J I 44Q 43 42 J g 38 r x I O l l F/G.4.

Patented Feb. 13, 1945 UNITED STATES INTERNAL-COMBUSTION ENGINE AlbertCollinson Nesileld, mm London,

. England Application February is, 1944, sci-nine. 522,865

In Great Britain January 19, 1943 13 Claims.

This invention relates to control of the flow ofgases in internalcombustion engines and more particularly to methods of and means forcontrolling the exhaust of internal combustion engines of the two-strokecycle type. x

In such engines it may be necessary or.advisable to maintain a valveopen to allow flow of gases for a very short period, for example, for aperiod comprising a small fraction. of a second. Owing to the inertia ofvalve members it has hitherto been impracticable to provide asatisfactorily operating controllable valve for this purpose.

The invention will be described hereinafter with reference to itsapplication to-the control of the exhaust gases of an internalcombustion engine of the two-stroke cycle type. In such engines thegenerally accepted theory of the condi-' tions which exist after theexplosion of a charge within a cylinder and the opening of the exhaustports is that there is a first period (hereinafter termed "first period)wherein a mass or body of burnt gase is discharged from the cylinder atvery high speed and on issuance sets up in the cylinder 9, high partialor almost complete vacuum. This body of burntga'ses then undergoes a toand fromoveme'nt of high frequency out of and into the cylinder due toits impact with the ga mass in the exhaust conduit which produces withinthe cylinder alternate negative and positive pressure fluctuations. Thisperiod of pressure fluctuations is followed as the gases pass throughthe exhaust conduit by a second period of substantially continuousdepression within the cylinder and this depression may be utilised, itan inlet valve is opened, to eil'ect the recharging of the cylinder.This latter depression is, however, somewhat less than the first initialdepression created during the first period above-mentioned and if theexhaust port canbe closed immediately after the moment of. primaryejection of the exhaust gases occurring in the above-mentioned firstperiod the higher depression then set up can be utilised moreadvantageously to recharge the cylin er.

Since t e time period during which the primary ejection of the exhaustgases in the socalled first period takes place may be of the order of0.0l'to 0.001 second after the opening of the exhaust ports it issubstantiall impossible to open and to close said ports within such ashort period owing to' valve inertia. The present in ventlon may beapplied to control the fiow of exhaust gases so that the exhaust periodis or the relatively small duration above-mentioned.

One object of the-present invention is to provide an operative cycle fortwo-stroke cycle en-' gines which utilises the depression'of theabovementioned first period for cylinder charging pur- Another object ofthe invention is to provide an improved" valve arrangement adapted toeffect exhaust cut-ofl' within'the time limits-of 0.01 to 0.001 secondafter opening of the exhaust valve 10 or port. Y

means for readily varying the'moment'of exhaust cut-oil in two-strokecycle engines. 'if desired, automatically in accordance w'ithithe enginespeed. s

In connection with, engines of the type hereinbefore referred tosuggestions have been made to interpose a one-way acting flap valve inthe exhaust conduit which shuts immediately on "reduction of pressurewithin the cylinder and provent the return flow of exhaust gases intothe cylinder after the first period of exhaust. such valves are,however, impracticable in continuous operation and are-not positivelycontrollable.- Other proposals have been to include positively drivenrotary valves in the exhaust conduit in cases where the econd period ofexhaust'fis being utilised for cylinder charging purposes. The term"main exhaust port'fiherein used is 30 intended to includea port orports in the cylinder wallcovered and uncovered by the reciprocatingpiston itself or by a sleeve valve or port controlled by anexternalpiston valve or by! rotary valve or by a valve of the poppet,type.

Further objects and advantages of my .inven tion'will be apparent fromthe following description' conslderedin coniunction with-theaccompanying drawings which =form a ,p'artpof' this specification and s:,which--&

Fig. 1 shows diagrammatically v of the invention toaninternal'cembustionongine cylinder having its parts controlled gby a:recip- 'rocat gpistom. I. V:'-"

Fig. 2 shows in vertical section internal combustion engineincorporating the valve ole-'- ment according to the invention:

Fig. 3 is a section on the line m-rn or'm. 2-

through the exhaust valve cani shaft transmia-M sion; o N

Fig. 4 shows a speed responsive governor applied to-the-arrangement ofFig. 3; and

Fig. 5 is a diagram showing themoments oi opening and closing of thevalves. in the improved two-stroke cycle.

Referring to the drawings. 1 shows dia- A further object of theinvention is to provide the application 4 I grammatically an enginecylinder l containing a reciprocating piston II, a series of exhaust 1ports I2 and a series of inlet ports IS. The exhaust portsi2'communicate with an exhaust conduit l4 and the inlet ports I3communicate withan admission conduit l5.

Located within exhaust conduit |4 adjacent the ports I2 is a valve I6 ofthe poppet type which is controlled as to its closing movement b meansof a spring ll and opened b means of a rocker arm I8 pivoted at l9 andcontrolled by'a cam 20. The cam 20 may, for example, be of the spiraltype having a substantially radial face 2| to allow rapid closing of thevalve under the influence of the spring II. To reduce friction a roller22 is preferably mounted on the arm It so as to contact with the face ofthe cam 20.

In operation, after the explosion of the charge within the cylinder illwith the piston moving downwardly within the cylinder as shown in Fig.1, the valve I is first opened so as to provide a free passagefor'exhaust gases when the piston I later uncovers the ports [2. At apredetermined moment after the opening of the exhaust ports l2 thepoppet valve I5 is closed by spring action owing to' the face 2| of thecam rotating opposite the roller 22 and substantially at the sameinstant exhaust valve it prevents any return surge of shaft 44; idlergear 42 inturn'meshes with the pinion 4| mounted on the cam shaft 40.

The device for adjusting the angular setting of the cam shaft comprisesa bush 44 rotatable with the pinion 4| by key connections and alsoslidable axially relative'to the pinion 4|. The bush 44 carries on itsinner periphery a pin (not visible in Fig. 3) which engages within ahelical groove 46 formed in the outer peripheral surface of the reducedend 41 of the cam shaft 40. The arrangement is such that axial movementof the bush 44 varies the angular setting of the cam shaft 40 relativelyto the-pinion 4| and thus relatively to the crank shaft 33 due to theinterengagement of the pin on the inner face of the bush with thehelical groove 46.

To eflect this axial movement of the bush 44 there is provided in theembodiment of Fig. 3 a

49 butnprevented from rotation by pins 5| 'on the collanengaging in aforked member 52 which pivots about a pin 53. The lower end 54 of mem-'gases passing back through "that portion of the 4 exhaust conduitdenoted by 23 from entering the cylinder and maintains the depressionwithin the cylinder, which at the moment ofopening of the inlet ports I3is automatically recharged by the inrush of the explosive charge throughthe admission conduit. |5. On the closure of the inlet ports H3 at asuitable moment by means of the piston H on. its upward compressionstroke, the

charge within the cylinder l0, due to its high velocity of entry, may beat a pressure above atmospheric.

Fig. 2 shows in vertical section a'practical embodiment of theinvention. shown the cylinder i0 containing theq pi stonll' includes anexhaust port or ports l2fan exhaust conduit l4, an auxiliary poppetvalve IS, a spring H, a rocker arm 3 and cam 20. In this embodiment aninlet port,30 in the cylinder head is controlled by an inlet valve 3!controlled as to closing by a spring 32 and opened by means of a rockerarm 33 pivoted about a pin 34 and actuated at its opposite end. 35through a transmission rod 33 by a cam 31 mounted on a cam shaft 18 androtated through suitable. gear transmission (not shown) from a gear 38mounted on the crank shaft 33.

The cam 20 is mounted on a cam shaft 40 "which carries a pinion meshingwithan idler gear 42 in turn meshing with the gear .33 mounted on thecrank shaft. The arrangement of these gears is shown more particularlyin Fig. 3.

Since the moment of closing of the exhaustpoppet valve I3 is offundamental importance means ,are provided for adjusting the said momentof closing by adjustment of the angular 7 setting of the cam shaft 40and cam 20. This 1 device is illustrated in Fig. 3 and shows the crankher 52, also'forked, engages in a groove 55 formed in the bush 44. Bythis means it is clear that rotation of the manipulating head 48 causesaxial movement of the collar 50, which axial movement is transferredthrough the member 52, 54 pivoting about the pin 53 to the bush 44.

Th/ provision of this manual adjustment enables an extremely finevariation of the setting ,of thepcam 20 and thus a very fine variationof the moment of closing of the auxiliary poppet valve l3. Thisadjustment will normally take place while the engine is running so thatthe setting of the cam 20 may be'varied to suit the particularcharacteristics of the individual engine. I

Since obviously the timing of the opening of I the exhaust valve willvary with variations'in the an automatic control responsive to the speedof the engine instead of the manual adjustable member 43above-mentioned. Such a device is shown 1 in Fig. 4 wherein the pinion4| driving the cam shaft 40 through the bush 44 and helical groovegovernor denoted generally by 6|. Governor 5| comprises a plate 62 ofcurved form and a further plate 63 mounted for free rotation on a stubshaft 64. The governor GI, 62 carries a number of, in the illustratedembodiment six, balls 55 mounted in radially directed grooves in theplate 53 which is urged by a spring 66 towards the plate 52 so as tomaintain the balls in contact with said plate 62. A lever 61 pivotingabout a pin 68 has a forked end 59 engaging a groove lli formed in aboss on the rear face of the plate 83 and is provided with a projectionH which engages within 4 52 sets up axial displacement of the plate 83and through the lever 61 and projection 1| moves the bush 44 axially inresponse to the engine speed. Adjustment of the position of the axiallymovable bush 44 varies the angular displacement of the cam shaft '40relatively to the crank shaft accord- This in turning to the speed ofthe engine. determines the moment of closing of the exhaust assumepoppet valve It, thus obtaining maximum emciency of operation over awide range of engine speed.

Since the cam shaft 18 carrying the cam I1 is preferably driven from thegear 38 mounted on cycle of the two-stroke cycle combustion engineshereinbefore described. Fig. shows the moments of opening and closing ofthe .exhaust and inlet valves with respect to crank shaft rotation. Forexample, the exhaust ports l2 may be opened at the point A in Fig. 5,approximately 120 after the top dead centre of the crank. The exhausttakes place during a period corresponding to a further crank rotation ofapproximately 30, at which point the auxiliary poppet valve I6 is closedas indicated by the point B. Substantially at this moment the inletvalve 31 (Fig. 2) is opened and the inlet valve is again closed when thecrank shaft has reached its bottom dead centre position as indicated bythe point C in Fig. 5. The inlet valve thus remains open during rotationof the crank shaft through about 30 but there may be a slight overlap inthe periods during which the exhaust poppet valve l2 and the inlet valve3| are open. That is to say, the inlet valve may. for example, be openedduring the last 5of crank prevent a return surge of gases into thecylinder through said main exhaust port.

3. An internal combustion engine of the twostroke cycle type having acylinder and an exhaust conduit which includes a main exhaust portcontrolling communication between said cylinder and said exhaustconduit, an auxiliary poppet valve located in said exhaust conduitadjacent said main exhaust port, means to open said main exhaust port,means to open said auxiliary popa pet valve operative prior to theopening of said main exhaust port, means to close said auxiliary poppetvalve to cut off communication between shaft rotation, during which theexhaust poppet valve 16 remains open. In any case the inlet valve is notopened until the outflow of exhaust gases from the cylinder during thesocalled first period of exhaust has substantially ceased.

While I have described and illustrated several embodiments of myinvention it is to be understood that this is for the purposeof-illustration only and that the scope of my invention is not to belimited thereby but is to be determined by the appended claims.

What I claim is:

1. That improvement in the operative cycle of an internal combustionengine of the two-stroke cycle type which consists in controlling thecommencement of the exhaust period by means of the normal exhaust ports,terminating the exhaust period substantially instantaneously by means ofan auxiliary cam actuated spring loaded valve and opening an inlet valvesubstantially at the moment of closing of said auxiliary valve, when theflow of exhaust gases from the cylinder at the end of the so-calledfirst period of exhaust has substantially ceased.

. 2. In an internal combustion engine of the two-stroke cycle typehaving an exhaust conduit and a main exhaust port providingcommunication between the engine cylinder and said conduit, the'methodof controlling the outflow of exhaust gases which consists in opening apositively spring actuatedauxiliary valve'located in said exhaustconduit adjacent the main exhaust port after the explosion of thecharge, subsequently opening said main exhaust port to allow ejection ofburnt gases into said exhaust conduit and closing said auxiliary valveat the termination of the so-called first period of exhaust to saidexhaust conduit and said cylinder and means responsive to the enginespeed to vary the moment of closing of said p pp t valve.

4. An internalcombustion engine of the twostroke cycle type having acylinder and an exhaust conduit which includesa main exhaust portcontrolling communication between said cylinder and said exhaustconduit, an auxiliary #095 pet valve located in said exhaust conduitadjacent.

said main exhaust port, means to open said main exhaust port, means toopen said auxiliary poppet valve operative priorto the opening of saidmain exhaust port, means to close said auxiliary poppet valve to out of!communication between said exhaust conduit and said-cylinder, an inletvalve and means to open said inlet valve sub- I stantially at the momentof closing of 'said poppet valve. 1 I

5. An internal combustion engine of the two stroke cycle type having acylinder and an exhaust conduit which includes a main exhaust portcontrolling communication between said cylinder and said exhaustconduit, an auxiliary poppet valve located in said exhaust conduitadjacent said main exhaust port,-a rotating shaft, a cam shaft having ahelical groove therein, a cam mounted on said shaft and positivelycontrolling the movement of said poppet valve, transmission meansdriving said cam shaft from said rotating shaft, a bush rotatable withand slidable axially relatively to said transmission, means, a

pin on said bush engaging in said helical groove and means to produceaxial movement of said bush and thereby to vary the angular setting ofsaid cam shaft and said cam. 6. An internal combustion engine ofthe'twostroke cycle type having a cylinder and an exhaust conduit whichincludes a main exhaust port controllingcommunication between saidcylinder and said exhaust conduit, an auxiliary poppet valve located insaid exhaust conduit adjacent said main exhaust port, means to open saidmain exhaust port, a rotating shaft, a cam shaft having a helical groovetherein, a cammounted on said shaft and positively controlling themovement of said poppet valve, transmission means driving said cam shaftfrom said rotating shaft, a bush rotatable with and slidable axiallyrelatively to said transmission means, a pin on said bush engaging insaid helical groove and means responsive'to the engine speed to produceaxial movement of said bush and thereby to vary the angular setting ofsaid cam shaft and said cam according to the speed of the engine.

7; An internal combustion engine of the twostroke cycle type having acylinder and an exhaust conduit which includes a main exhaust port'controlling communicationbetween said cylinder and said exhaust conduit,an auxiliary poppet valve located in said exhaust conduit adjacent saidmain exhaust port, means to open said main exhaust port, a rotatingshaft, a cam shaft having a helical groove therein, a cam mounted onsaid shaft and positively controlling the movement of said poppet,valve, transmission means .driving said cam shaft from said rotatingshaft,

a bush rotatable with and slidable axially relatively to saidtransmission means, a pin on said bush engaging in said helical groove,means to produce axial movement of said bush and thereby to vary theangular setting of said cam shaft and said cam, an inlet valve and meansto open said inlet valve substantially at the moment of closing of saidpoppet valve.

8. An internal combustion engine of the twostroke cycle type having acylinderand an exhaust conduit which includes a main exhaust portcontrolling communication between said cylinder and said exhaustconduit, an auxiliary poppet valve located in said exhaust conduitadjacent said main exhaust port, means to open said main exhaust port,arotating shaft, a cam shaft having a helical groove therein, a cammounted on said shaft and positively controlling the movement of saidpoppet valve, transmission means driving said cam shaft from saidrotating shaft, a bush rotatable with and slidable of closing of saidpoppet valve, and means to vary the moment of opening of said inletvalve.

10. An internal combustion engineof the twostroke cycle type havingacylinder and an exhaust conduit which includes a main exhaust portcontrolling communication between said cylinder and said exhaustconduit, an auxiliary 7 said bush engaging in said helical groove and aspeed responsive governor producing axial movement of said bush andthereby varying the anaxially relatively to said transmission means, a

I haust conduit which includes a main exhaustport controllingcommunication between said cylinderand said exhaust conduit, anauxiliary poppet valve located in said exhaust conduit adjacent saidmain exhaust port, means to open said main exhaust port, a rotatingshaft, a cam shaft having a helical groove therein, a cam mounted onsaid shaft andpositively controlling the movement of said'poppet valve,transmission means driving said cam shaft from said rotating shaft, abush rotatable with-and slidable axially relatively to said transmissionmeans, a pin ;on' said bush engaging in said helical groove, means toproduce axial movement of said bush and thereby to vary the angularsetting of said cam shaft and said cam, an inlet valve, means to opensaid inlet valve substantially at the moment gular setting of said camshaft and said cam.

11. That improvement in the .operative cycle of an internal combustionengine of the twostroke cycle type which consists in controlling thecommencement of the exhaust period by means of the normal exhaust ports,terminating the exhaust period by means of an auxiliary springcontrolled, valve and opening .an inlet valve substantially at themoment of closing of said auxiliary valve, when the flow of exhaustgases from the cylinder at the end of the socalled first period ofexhausthas substantially ceased.

12. 'An internal combustion engine of the twostroke cycle type whichincludes a main exhaust port and an auxiliary spring-actuated valvearranged in seriesin the path of fiow of the exhaust gases and cammeans. cooperating with said actuating spring to provide approximateinstantaneous closing of said auxiliary valve by said springsubstantially at the instant of termination of the so-called firstperiod of exhaust.

13. An internal combustion engine of the twostroke cycle type whichincludes a main exhaust port and an auxiliary spring-actuated valvearranged in series in the path of fiow of the ex-' haust gases, cammeans cooperating with said actuating spring to provide approximateinstan taneous closing of said auxiliary valve by said springsubstantially at the instant of termination of the so-called first.period of exhaust and means for varying the moment. of closing of saidauxiliary valve. I

ALBERT coLLINsoN NESFIELD.

